Electrically driven sewing machine control apparatus

Abstract

A motor control apparatus for driving a power sewing machine comprises a main motor circuit for supplying a motor current to a DC motor from an AC power supply through a main switch and a semiconductor element with a control electrode, a controller for controlling the speed of the motor, a first control means for effecting normal stitching by controlling the conduction state of the semiconductor element, a second control means for effecting a single stitch by controlling the conduction state of the semiconductor element, and a means for switching the operation between the first and second control means. The second control means includes a needle position detector means for detecting the needle to reach predetermined positions, a switching means connected in series to the needle position detector means, a trigger voltage supply means for applying a trigger voltage to the control electrode of the semiconductor element, and a switch-operating means. The switch-operating means operates in such a manner that, when the main switch is closed without the depression of the controller, the switching means is closed, while upon the depression of the controller, the switching means is opened for predetermined time and thereafter to close again upon the lapse of said predetermined time. If the needle position detector means detects that the needle has reached the predetermined positions with the switching means closed, the trigger voltage supply means is made ineffective.

We claim: 
     
       1. A control apparatus for a motor for driving a power sewing machine comprising: a main motor circuit for supplying a motor current to a DC motor from an AC power supply through a main switch and a semiconductor element with a control electrode;   a controller for controlling the speed of said motor, said controller being movable between a first and a second position and normally biased toward said first position and having a first resistor with two terminals, the resistance between said two terminals of said first resistor being continuously changeable between a first and a second value and having said first and second values when said controller is set to said first and second positions respectively, and one of said two terminals of said first resistor being connected to said AC power supply;   first means for producing a first trigger voltage, said first means having an input connected to the other of said two terminals of said first resistor and an output connected to said control electrode of said semiconductor element, and said first trigger voltage being controlled by changing the resistance of said first resistor thereby controlling the firing angle of said semiconductor element;   second means for applying a second trigger voltage to said control electrode of said semiconductor element;   switch means alternatively changeable between a first and a second state, said first and second means being rendered inoperative when said switch means is changed to said first and second states respectively;   needle position detector means adapted to be actuated when a needle reaches predetermined positions;   a time-constant circuit having a second resistor with two terminals and a capacitor, one of said two terminals of said second resistor being connected to said the other terminal of said first resistor, and said capacitor being connected across at least a portion of said second resistor;   a solenoid connected to said time-constant circuit; rectifier means for rectifying the power voltage of said power supply and applying the rectified power voltage between said one terminal of said first resistor and the other of said two terminals of said second resistor, said rectifier means being actuated when said main switch is closed and said switch means is changed to said first state;   the terminal voltage of said capacitor being set, when said rectifier means is actuated, to a first voltage when said resistance of said first resistor is set to said first value and changing with a predetermined time-constant from said first voltage to a second voltage when said resistance of said first resistor is set to said second value against said biasing force;   said solenoid being actuated during the time in which said terminal voltage of said capacitor changes from said first voltage to said second voltage;   third means for rendering said second means inoperative in response to the actuation of both of said needle position detector means and said solenoid.     
     
     
       2. A control apparatus for a motor for driving a power sewing machine according to claim 1, wherein said first value of said first resistor being higher than said second value thereof, said terminal voltage of said capacitor increasing with a predetermined time-constant from said first voltage to said second voltage higher than said first voltage when said resistance of said first resistor is set to said second value thereby charging said capacitor during the time in which said terminal voltage of said capacitor increases from said first voltage to said second voltage, and said solenoid being actuated while said capacitor is charged. 
     
     
       3. A control apparatus for a motor for driving a power sewing machine according to claim 2, wherein said solenoid being connected across said rectifier means and deenergized while said capacitor is charged.